In some bodies of water, the water level can fluctuate between a high water mark and a low water mark multiple times per day due to the tides. Water levels can also fluctuate in non-tidal bodies of water, for example in power generating lakes where water may be drawn down for hydro-electric power generation at higher usage times, or seasonally. Tidal or other water level changes can have an amplitude of over six feet and a wavelength of a little over twelve hours. In these areas a dock at a fixed height can be impractical for many applications. A fixed dock results in a large vertical distance between the deck and the water surface at low tide. Boats tied off to a fixed dock may need to be continuously retied as the tide changes. Therefore, docks often employ a floating marine structure designed to change vertical position as the water level rises and falls.
Previously known floating marine structures, or floating docks, include a buoyant horizontal deck that is secured to the shore or a fixed structure, for example by a hinged walkway or pier. The deck is secured in a way that allows it float on the water surface and move freely in a vertical direction as the water level changes. However, in addition to more gradual longer-term and/or larger-scale water level changes such as tidal changes, the water level is also subject to sudden shorter-term fluctuations. Passing boats create wakes and wind or other weather can create chop. These conditions create waves of a smaller amplitude than the tides, but also of a much smaller wavelength and/or higher frequency, often lasting only a few seconds. These smaller, but sharper waves can cause damage to the floating dock and objects secured to it when the floating dock is allowed to move freely. Sudden changes in the floating dock's vertical position can also compromise the comfort and safety of persons on the dock.
Accordingly, it can be seen that needs exist for a floating marine structure capable of adjusting vertical position when subject to large, gradual changes in water level, but remaining relatively stable in a fixed vertical position when subjected to smaller waves. It is to the provision of a hybrid fixed/floating dock or other marine structure meeting these and other needs that the present invention is primarily directed.